Fluxes for Aluminum Smelter are indispensable auxiliary materials in the smelting process of secondary aluminum smelting process. In addition to being used as a covering agent, it is more important as a refining agent and a modifier. The basic requirements of the fluxes for aluminum smelter: the melting point is lower than that of aluminum and aluminum alloys, and its density is smaller than that of aluminum and aluminum alloys. It should not react with furnace gas, furnace lining, molten aluminum, and aluminum alloys. At the same time, the flux has good wettability to the oxide film and is cheap easy.
Generally, the melting point of the aluminum casting flux is required to be lower than the melting temperature of aluminum and aluminum alloy, so that the covering flux can cover the surface of the aluminum and aluminum alloy melt in a liquid state. Commonly used single chloride salt and fluorine salt have a higher melting point than aluminum and aluminum alloys. Therefore, a mixed salt that can be in a eutectic state or a solid solution state is selected as a flux. Sodium chloride and potassium chloride can form a fusible eutectic salt.
The melting point of the eutectic composition of 55% KCl and 45% NlCl is 650℃, which can maintain the liquid level with good fluidity at the melting temperature of aluminum alloy. The liquid density of the mixed salt is 1.5g/cm3, which is lower than the density of molten aluminum (2.42.5g/cm3), so it can better cover the surface of aluminum and aluminum alloy melts. The binary salt has good chemical stability, does not chemically react with molten aluminum, and has a certain ability to dissolve aluminum oxide inclusions and hydrogen from aluminum and aluminum alloy melts. Therefore, the eutectic mixed salt of sodium chloride and potassium chloride is often used as the basic component of aluminum and aluminum alloy fluxes.
In order to improve the properties of the flux, additional ingredients need to be added. On the basis of the eutectic chloride salt, an appropriate amount of fluoride salt, such as sodium fluoride, calcium fluoride, cryolite, etc., can be added to enhance the ability of the flux to dissolve oxides, especially alumina. The addition of fluoride salt can also increase the wettability of the flux to alumina, thereby improving its adsorption capacity, and at the same time increase the surface tension of the flux, which is easy to separate from the aluminum and aluminum alloy melts, and reduce the possibility of mixing into the flux.